Thermoplastic compositions of watersoluble cellulose ethers



Unit S ates Patm O 2,s40,4ss

THERMOPLASTIC COMPOSITIONS OF WATER- SOLUBLE CELLULOSE ETHERS George K.Greminger, Jr., Midland, and Miles A. Weaver,

Ithaca, Mich., assignors to The Dow Chemical Company, Midland, Mich., acorporation of Delaware No Drawing. Application November 25, 1953 SerialN- 394,476

8 Claims. (Cl. 106182) This invention relates to thermoplastic,water-soluble compositions of certain cellulose ethers.

Methods for fabricating useful articles from watersoluble celluloseethers have been limited to casting and dipping from aqueous solutions.Because of the unique solubility characteristics of those ethers manydifliculties arose when it was attempted to use such methods. Forexample, the temperature of the solution had to remain below the gelpoint of the cellulose ether during the shaping operation. Anotherobjection was that the amount of cellulose ether in solution had to berestricted because the viscosity of the solution had to be low enoughfor casting or dipping operations. A still further objection was thedifliculty in dissolving sufiicient amounts of the higher viscositygrades of the ethers. Therefore, so that the cellulose ethers may beused in a wider variety of applications for which their properties areideally suited, it has long been desired to find a thermoplasticwater-soluble cellulose ether composition which could be thermallyfabricated. One such composition has been disclosed by Silvernail in U.S. Patent 2,602,755. That composition consisted of a water-solublecellulose ether, propylene glycol, and glycerine in certain statedproportions.

It is an object of this invention to provide watersoluble compositionsof cellulose ethers, which compositions are capable of being thermallyfabricated.

It has now been found that thermoplastic composi tions may be preparedby mixing or blending cellulose ethers with an alkyl glycolate in whichthe alkyl group contains from 1 to 4 carbon atoms. Although thesecompositions are especially well adapted for thermal fabrication, theymay also be used in conventional casting and dipping operations. 2

The cellulose ethers that are useful in the compositions of thisinvention are water-soluble alkyl, hydroxyalkyl, or alkyl hydroxyalkylcellulose ethers in which the alkyl group may contain from 1 to 3 carbonatoms and in which the hydroxyalkyl group may contain from 2 to 3 carbonatoms. Of particular usefulness are methyl cellulose, hydroxypropylcellulose, and methyl hydroxypropyl cellulose.

It is not critical in the compositions of this invention 7 that theaforementioned ethers exhibit thermoplasticity in themselves. The chiefrequirement for use in this invention, besides the previously mentionedstructural limitations, is water solubility. It is well-known thatmethyl cellulose, and other cellulose ethers which are soluble inaqueous media, differ in their solubility properties depending on theextent to which they are etherified. The least etherified products aresoluble only in dilute alkaline media, and often only at lowtemperatures. The somewhat more highly etherified materials are solublein water. In a few cases the fully etherified compounds become insolublein water and are soluble only in organic solvents. Also, certain alkylhydroxyalkyl cellulose ethers, such as those described in our 2copending application Serial No. 394,484,-fi1ed Novem ber 25, 1953, aresoluble in both aqueous and organic media.

Any of the commercially available'viscosity. grades of these celluloseethers may be employed. The vis- 'cosity grade used will depend chieflyon the properties desired in the fabricated article and on otherpractical considerations such as the length of time required to blendtheethers with the plasticizer., The higher the intrinsic viscosity ofthe cellulose ether, the less fluid will be the composition and thelonger will be the time required to mix in the plasticizer.

As previously mentioned, the useful plasticizers for the compositions ofthis invention are alkyl glycolates in which the alkyl group containsfrom 1 to 4 carbon atoms.

Other known plasticizers for cellulose ethers may be used in conjunctionwith the alkyl glycolates of this invention. mentioned propylene glycoland acetyl tributyl citrate. Their use is not essential, however, inpreparing the thermoplastic compositions. The useful compositions arethose containing from about 5 to about 80 percent by weight of thecellulose ether and correspondingly from about 95 to about 20 percent byweight of the alkyl glycolate. When less than about 5 percent cellu--lose ether is present, there is usually insuflicient body to thecomposition for fabrication and articles prepared therefrom are verythin in cross-section .and weak. When the compositions contain more than80 percent of cellulose ether, the compositions are so stiff andincompletely plasticized as to make fabrication unnecessarily diflicultand to cause the resulting articles to be brittle. The amount that isused in any particular composition will depend on the viscosity grade ofthe cellulose derivative, and on the intended use of the composition. Itshould be obvious that when the very high viscosity grades of celluloseethers (4000 centipoises or higher) are used, high concentrations of thecellulose ether are impractical because the resulting solutions are soviscous that they cannot be easily worked. Also, the fluidity of theplasticized composition that is necessary varies with the type offabricating operation. For casting and dipping operations, the solutionsmust have greater fluidity than with most thermal operations, suchas'injection molding or extrusion. When reference is made herein to theviscosity grade of the cellulose ether, this is the viscosity incentipoises of a 2 percent solution of that ether by weight in water at20 C.

The compositions of the invention will be further defined by thefollowing illustrative example.

Example 1 Equal parts by weight of a water-soluble methyl hydroxypropylcellulose and isopropyl glycolate were mixed together. The resultingcomposition was compression molded at 138 C .and 1770 pounds per squareinch gauge. The resulting sheet had excellent clarity and gloss and hadhigh elongation and tensile strength.

ce Patented June 24, 1958 As examples of such plasticizers may be I centof an alkyl glycolatein which the alkyl group 7. The composition claimedin claim 1, wherein the contains from 1 to 4 carbon atoms. 7 alkylg-lycolate'is isobutyl glycolate.

2. The composition claimed in claim 1, wherein the 8. The compositionclaimed in claim 1, wherein the cellulose ether is a water solublemethyl cellulose. alkyl glycolate is allyl glycolate.

3'.The compositiomclaimed inclaim 1; wherein; the" 5 cellulose ether isa water-soluble=methyl hydroxypropyl References Clted i file of thls P gI. d 1 h UNITED STATES PATENTS.

e*c'ompos1t1on=ca1me mc'a1mw ereinj e cellulose ether is a, watersoluhle hydroxyetl'iyl cellulose: 188O513 Stand et 1932 5 The comositionclaimed' in claim-1 wherein the 10 2122716 Graves July 1938 P t v2,388;l64 Loder i Oct. 30,1945

alkyl glycolate is ethyl"glycolate:

6. The composition claimed" in claim 1, whereinv the FOREIGN PATENTSalkyl glycolateis isopropylglycolate; i I 311,664 Great Britain May 8,1929

1. A THERMOPLASTIC COMPOSITION CONSISTING ESSENTIALLY OF FROM 5 TO 80PERCENT OF A WATER-SOLUBLE CELLULOSE ETHER SELECTED FROM THE GROUP OFALYL CELLULOSE, HYDROXYALKYL CELLULOSE, AND ALKYL HYDROXYALKYL CELLULOSEIN WHICH THE ALKYL GROUP CONTAINS FROM 1 TO 3 CARBON ATOMS AND THEHYDROXYALKYL GROUP CONTAINS FROM 2 TO 3 CARBON ATOMS, ANDCORRESPONDINGLY FROM 95 TO 20 PERCENT OF AN ALKYL GLYCOLATE IN WHICH THEALKYL GROUP CONTAINS FROM 1 TO 4 CARBON ATOMS.